Emulsions which contain essentially tabular silver halide grains are well known in the prior art. These grains provide some advantages over more conventional, spherical grains. For example, silver halide X-ray elements containing tabular grains can be fully forehardened and yet maintain excellent covering power. This is an advantage over conventional X-ray elements containing spherical grains which are normally hardened during the processing steps. Additionally, tabular grains can be coated at a lower coating weight and thus have a silver savings over elements containing conventional grains. Also, elements containing tabular grains sometimes exhibit a higher speed than those with spherical grains. Sometimes, however, elements made using these tabular grains have lower covering power and lower gradient than those made with spherical grains, for example. Additionally, there are always needs to reduce silver halide coating weights still further in order to save on silver costs.
The use of various thiones within a silver halide element is also known. For example, heterocyclic thiones have been added in combination with other ingredients in order to increase the speed or reduce the color gradient within color emulsions, for example. None of these references disclose the addition of these compounds to tabular grain emulsions in order to increase the contrast and covering power thereof.